1. Field of the Invention
This invention relates to a process for saccharification of rootstocks and subsequent alcohol fermentation. More particularly it relates to a process for saccharifying rootstocks such as sweet potatoes, cassave roots and white potatoes according to an enzymatic processing without conventional steaming, and using the resulting material as a feed substrate for alcohol fermentation.
2. Description of the Prior Art
Fossil energy resources have been getting scarcer, and as a countermeasure to this, conversion of renewable resources i.e. biomass into energy resources and utilization of biomass as chemical raw materials have recently come to public notice.
Heretofore, according to conventional processes for saccharification of rootstocks such as sweet potatoes. Cassava roots, white potatoes, etc. and subsequent alcohol fermentation, such raw materials have been once cooked for gelatinization of starch followed by adding .alpha.-amylase to act on the gelatinized starch to convert it into dextrin, which, in turn, has been subjected to alcohol fermentation.
However, such conventional processes have had drawbacks in that large scale equipments such as high pressure cookers have been required and also a large quantity of heat has been needed for cooking. In particular, such a quantity of heat and that required for distilling off ethanol from the fermented beer for alcohol has increased the amount of heat required for the overall process of ethanol fermentation, whereby no commercially effective process could have been achieved. For example, conventional cooking of rootstocks to gelatinize starch for saccharification proceeding to subsequent alcohol fermentation has been carried out under pressure of about 2.5 kg/cm.sup.2 for about 30 to 60 minutes and the quantity of steam required for the heating has amounted to about 30% of the total quantity of steam required for alcohol production. Further, drain mixes in the material during the cooking treatment, whereby the feed substrate for alcohol is diluted to reduce the concentration of the alcohol obtained by fermentation. Furthermore, a quantity of heat required for alcohol distillation carried out in the final step is increased and the yield of the product alcohol per unit of a quantity of heat is reduced. According to the conventional processes, the heat energy required for the alcohol distillation has amounted to as large as 1/2 of the combustion energy of the alcohol.